Re: prefix btree implementation

"Bricklen Anderson" <BAnderson@PresiNET.com> wrote
>
> Oracle implements something similar called index compression, but I 
> believe it
> is only for common column values. I haven't checked in versions>9r1 so 
> maybe
> there are other options implemented by now.
>
> Jonathan Lewis describes some pros and cons here:
> http://www.jlcomp.demon.co.uk/faq/compress_ind.html
>

Oracle 9 uses the grammar like this:
   CREATE INDEX ... [ COMPRESS <number_of_first_columns> ]

So it gives the flexibility of choosing optimal number of coulumns to the 
user. The script mentioned in the article guesses the optimal number by 
estimating the size of each choice. But I am thinking we can do it better: 
(1) we don't require that the compressed number of columns on each page are 
the same; (2) when we build up index bottom-up, we can determine this number 
for each page automatically by maximizing the number of items within a page.

Regards,
Qingqing